Accumulation modes and effects of differentially charged polystyrene nano/microplastics in water spinach (Ipomoea aquatica F.)

There is widespread concern about the risk of nano/microplastics (N/MPs) entering the food chain through higher plants. However, the primary factors that influence the absorption of N/MPs by higher plants remain largely unclear. This study examined the impact of Europium-doped N/MPs with different particle sizes and surface charges by water spinach (Ipomoea aquatica F.) to address this knowledge gap. N/MPs were visualized and quantitatively analyzed using laser confocal microscopy, scanning electron microscopy, and inductively coupled plasma-mass spectrometry. N/MPs with different surface charges were absorbed by the roots, with the apoplastic pathway as the major route of transport. After 28 days of exposure to 50 mg L^-1 N/MPs, N/MPs-COOH caused the highest levels of oxidative stress and damage to the roots. The plants accumulated NPs-COOH the most (average 1,640.16 mg L^-1), while they accumulated NPs-NH₂ the least (average 253.70 mg L^-1). Particle size was the main factor influencing the translocation of N/MPs from the root to the stem, while the Zeta potential mainly influenced particle entry into the roots from the hydroponic solution as well as stem-to-leaf translocation. Different charged N/MPs induced osmotic stress in the roots. A small amount of N/MPs in the leaves significantly stimulated the production of chlorophyll, while excessive N/MPs significantly reduced its content. These results provide new insights into the mechanism of interaction between N/MPs and plants.